The present relates to a vehicle steering assembly with an improved gear for retaining a steering wheel assembly on a steering column shaft.
Before the introduction of airbags, steering wheel assemblies could be easily attached to a steering column shaft. Access to the column shaft through a steering wheel assembly was made through the hub of the steering wheel assembly from the front face of the steering wheel assembly.
Airbag assemblies for a driver of a vehicle are typically located on the hub of a steering wheel assembly. Thus, access to a steering column shaft through the hub of a steering wheel assembly has become more difficult. Some methods of attaching a steering wheel and airbag assembly to a steering column shaft require a two step process. A steering wheel assembly is initially attached to a steering column shaft. An airbag assembly is then attached to the steering wheel assembly.
In order to reduce assembly time and labor costs, a modular steering wheel and airbag combination was developed. The modular steering wheel and airbag combination comprises a steering wheel armature and a separate hub plate. An airbag assembly is attached to the hub plate to form a hub plate subassembly. The hub plate subassembly is then attached to a steering wheel assembly including the steering wheel armature.
A structure for securing the steering wheel and airbag combination is accessible from the rear face of the combination. The hub plate is welded or intregal with a hub having a bore into which a steering wheel shaft can be inserted. A gear, preferably a helical gear having a gear portion with angled teeth, is disposed within the bore of the hub. The bore through the hub includes an upper cavity of increased diameter on the rest of the bore, thereby creating a bearing surface upon which the gear rests. The gear also includes threads complementary to threads on an outer end of the steering column shaft. A worm is adapted to drive the helical gear to secure the helical gear to the steering column shaft, thereby retaining the hub to the outer end of the steering column shaft. This structure is described in further detail in copending U.S. application Ser. No. 08/522,627 filed Sept. 1, 1995, the assignee of which is the assignee of the present invention.
To remove the steering wheel assembly, the worm drives the helical gear in the opposite direction, drawing the gear axially away from the steering column shaft. The helical gear assists in forcing the hub plate away from the steering column shaft by impinging on the back of the airbag inflator. During removal, the force required to remove the steering wheel assembly from the steering column shaft can be extremely high, particularly if the steering wheel assembly includes a "wedge lock" between the hub and steering column shaft or if the steering wheel assembly has been assembled on the steering column shaft for many years. This results in equally high torque at the shaft for removal, which current gears and worm tools are unable to provide without significant risk of failure.